When used as part of an impact tool, such as a hammer, axe, hatchet, pick, or shovel, the handle must be securely gripped to apply maximum force and to maintain control of the tool during use. However, upon impact, vibration is transmitted from the impact end of the tool handle along the tool handle to the grip end that is held by the user. Reduction of vibration frequency and/or vibration duration decreases painful vibration to the user's hand and arm and permits the user to maintain a tight grasp on the grip end of the handle. The user is thus able to maintain better control over the tool during and after impact.
Over the years, reduction of vibration has been sought in tool handles for impact tools. In U.S. Pat. No. 1,401,896, metal wire was wrapped around a reduced wooden handle to produce elasticity or resilience and reduce shock or injury to the hand of the user. U.S. Pat. No. 479,032 also discloses a hammer handle made of a metal core with metal wire coiled around the core. Metal wire is also used around the handles disclosed in U.S. Pat. No. 2,155,804 to reinforce a wooden handle. Another example of wire wrapped around a tool handle is disclosed in U.S. Pat. No. 1,341,378.
Tool handles made from synthetic resins, particularly composite materials, have replaced wooden handles in many applications because of their superior strength and durability. Such tool handles and their compositions are known in the art as disclosed in U.S. Pat. Nos. 3,770,033, 5,375,486, 5,588,343, and 5,657,674, all herein incorporated by reference. However, the vibration transmitted to the user of non-wood handles is higher. This is especially true with hammers having internal metal cores surrounded by a molded plastic shell. The vibration dampening property of non-wood handles can be one hundred to one thousand times less than a comparable wood handle.
Prolonged use of such non-wood handles can quickly tire the hand and arm muscles of the user. Besides affecting the comfort and productivity of the user, extended use can result in physiological damage to the hand, arm, and/or shoulder of the user.
U.S. Pat. No. 5,348,360 discloses a common method of reducing vibration by means of a soft material around the sections of the handle that are held by the user. These gripping devices cushion the user's hand against vibration and abrasion. To be effective, the devices must be held by the user during use of the tool. These devices are typically attached to the external surface of the tool handle by means of adhesives. As noted in the reference, such devices become worn the extent that they require periodic replacement so the design and attachment of the material must accommodate removal and replacement.
U.S. Pat. No. 5,588,343 relates to a handle having core member and synthetic resin sleeve wherein the core member has a channel therein extending from the grip end over a portion of its length. U.S. Pat. No. 5,657,674 discloses a body of a hammer that includes an elongated member with a cradle connected to and extending generally normal to the elongated member. In U.S. Pat. No. 5,704,259, a tuned vibration absorber is attached to the handle to reduce vibration. U.S. Pat. No. 5,772,541 adds a chamber on an implement with a handle and a freely movable elastomeric member disposed in the chamber to reduce vibration. The handle disclosed in U.S. Pat. No. 5,911,795 has spaced apertures along the length of its core member and a vibration dampening canister in the handle.
The means for vibration dampening disclosed in the prior art require significant changes and/or additions to the design of the tool handle. These changes and additions increase the cost and complexity of manufacture. Addition of elements to the handle may increase the size and weight of the handle and the likelihood that the elements will be damaged during use of the tool.
The tool handles according to the invention reduce vibration frequency and/or vibration duration. They do not require additional constructions such as canisters or channels to tool handle so extensive re-design of tool handles and methods of manufacture that are currently available is not required. Unlike the soft cushioning devices of the prior art, the tool handles do not become easily 30 worn or require replacement. The attractive aesthetic appearance of the tool handle can be varied while maintaining the advantageous vibration dampening properties.